# Surface tension boats

by dontregartha September 28, 2017

Explore surface tension with this fun and simple activity.

### You will be able to:

• Explore surface tension practically
• Design experiments to determine what makes the fastest surface tension boat.
• Make links to Newtons 3rd Law of Motion.

### You will need:

• 1 x Gratnells A3 (D3) or Art (A1) tray
• Tap water
• 10ml washing up liquid or liquid soap in a small beaker or Gratnells mini tray
• 2 x 3ml plastic pipette
• 1 x Recycled piece of thick card about A5 in size to make a boat
• 1 x scissors
• 1 x stopwatch (optional)
• Camera or video recording equipment (optional)

### What to do:

• Place the A3 or Art tray on a flat surface and fill to ~3cm deep with tap water.
• Cut out two boats from recycled thick card using the template provided.
• Start your video recording device (optional).
• Gently float both boats on the surface of the water at one edge of the tray, evenly space them to ensure each boat has space around it. Be careful not to disrupt the surface.
• Using the plastic pipettes, simultaneously place one drop of liquid soap into the central reservoir space of each boat.
• Observe the effect on the boats.
• Optional: Time how long it takes for your boat to reach the other side of the tray.

### What is happening?

When the boat is placed gently on the surface of the water, it rests on the surface and is suspended by surface tension. Upon putting a drop of soap solution (detergent) into the reservoir space, the boat accelerates rapidly and stops only when it hits the tray wall. Soap molecules try to spread (disperse) evenly over the surface of the water. Since they are confined in the central reservoir of the boat, their only way out is through the narrow rear channel. Rapid movement of the soap molecules through the narrow channel creates a directional force which drives the boat forward. This is also linked to Newton’s 3rd Law of Motion; for every action, there is an equal and opposite reaction, i.e. soap molecules go one way, the boat goes the other.

### Other things to try…

#### There are lots of potential variables you could investigate:

• Size of boat
• The material of boat – e.g. thick card, thin polystyrene, corriflute
• Size and shape of the central reservoir and channel
• Brand of soap
• Concentration of soap